In the drilling of bore holes into or through earth formation, such as, for example, in the drilling of oil or gas wells, utilizing a rotary drill bit, it may occur, from time to time, that the bit may be stuck in the earth formation or debris in the bore hole, either due to the caving in of the bore hole wall, or due to the formation of a key seat in the hard earth formation. When the bit is stuck, under such circumstances, it is difficult, if not impossible, to pull the drill string and bit from the bore hole. In the case of drilling by the usual rotary method, wherein the drill bit is attached to the lower end of a rotary string of drill pipe, it is an easy matter to rotate the drill pipe by the usual rotary table as an upward pull is being applied to the drill pipe, to assist in the release of the stuck bit.
In the case of in-hole motor drill assemblies of the electrical or fluid motor types wherein the rotary drill bit is driven by the in-hole motor interposed between the running string and the bit, it is not, as a rule, possible to cause the bit to rotate by rotation of the running drill or pipe string or fluid conduit above the motor. The reaction torque of such in-hole motors is, generally, taken by a rotary table at the surface of the bore hole, whereby the drill pipe string can either be held stationary or, if desired, rotated to obviate the wedging of the string. However, if the bit becomes stuck in the bore hole, such in-hole motors will stall and continued rotation of the bit may not be possible, notwithstanding the availability of additional drilling fluid pressure. When such motor drills are stalled in the bore hole, rotation of the drill pipe string by the rotary table is ineffective to cause bit rotation, since there is no positive drive between the stator and the rotor and the bit remains wedged, or stuck, in the hole. As a consequence, when an in-hole motor drill has the drill bit stuck in the bore hole, the only recourse has been to attempt to pull the running pipe string and the motor drill from the bore hole, without rotating the bit, and various jarring devices have been utilized in the drill pipe string to assist in applying upward jarring forces to the drill pipe string and to the bit, in an effort to dislodge the latter.
In the event that the bit remains stuck, the only recourse is to break the drill pipe joint above the motor drill assembly, if possible, in a known manner, whereby the drill pipe string can be retrieved to the drilling rig and, thereafter, to sidetrack the bore hole around the motor and bit which remain in the hole. Such practices result in great losses in time and costs.